$400 for my JG G36C
$75 for a 551 Holographic Sight
$200 for a WE Hi-Capa 4.3

for a "Canada legal" gun, you have to keep in mind that you should downgrade ASAP to about 350fps so that it is fieldable at 90% of games. And doesn't break down as fast.
$10 for spring
$__if you want to pay someone to do it, zero to do so yourself.